JP3451643B2 - Color image forming equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus in which a plurality of color toner images are superimposed on an intermediate transfer member and then transferred collectively on recording paper. In recent years, an electrophotographic recording system has been used for a color printer, a color facsimile, a color copying machine, and the like. In an electrophotographic recording apparatus using this system, a latent image formed on a photosensitive member is sequentially colored. A process of developing with a different color toner, repeating the process of once transferring the developed toner image to the intermediate transfer body in the order in which the developed toner images are developed, forming an entire toner image on the intermediate transfer body, and then transferring the image to recording paper. There is. As is well known, this electrophotographic recording apparatus includes an image forming process and a recording paper conveying process. The image forming process includes an electrostatic latent image forming process, an electrostatic latent image developing process, and a transfer process. Process and fusing process. In the process of forming an electrostatic latent image, an electrostatic latent image is formed by optically projecting an image on a photosensitive drum or a photosensitive belt, or by applying a charge on a dielectric drum. In the electrostatic latent image developing process, the electrostatic latent image is developed by electrostatically attaching toner as a recording medium to the electrostatic latent image formed as described above. In the transfer process, the toner image developed as described above is transferred to the recording paper by applying a voltage having a polarity opposite to that of the toner to the recording paper, and in the fixing process, the toner image transferred to the recording paper is melted by heat or the like. Fix on recording paper. Incidentally, when a plurality of color toner images are superimposed on an intermediate transfer member and then transferred collectively on recording paper, it is necessary that color misregistration does not occur in any area within one page. . FIG. 7 is a view for explaining a configuration example of a color image forming apparatus. FIG. 7 shows a case where an intermediate transfer belt 6 is used as an intermediate transfer member, and includes a photosensitive drum 1, a driving roller 8, stretching rollers 9 and 10, and transfer rollers 11a and 11b.
The charger 2 first uniformly charges the photosensitive drum 1 to, for example, about -700 V under the control of a control unit (not shown). Next, the rotating photosensitive drum 1 is scanned as shown by an arrow B by, for example, a laser beam sent from the exposure unit 4 as shown by an arrow A to form an electrostatic latent image. The image is developed by attaching color toners by the developing units 3a to 3d. The developing unit 3a has a yellow toner, the developing unit 3b has a magenta toner, the developing unit 3c has a cyan toner, and the developing unit 3d has a black toner. The toner image transferred to the intermediate transfer belt 6 and developed with magenta by the next rotation is transferred to the intermediate transfer belt 6,
Next, the toner image developed in cyan is transferred to the intermediate transfer belt 6, and the toner image developed in black is then transferred to the intermediate transfer belt 6.
Transfer to That is, the intermediate transfer belt 6 is driven and driven by the drive roller 8 as shown by the arrow C, and the transfer roller 1
A voltage having a polarity opposite to that of the toner, for example, about 2 KV is applied by 1a and 11b, and the toner image is transferred by attracting the toner at a contact point with the photosensitive drum 1. Then, the residual toner on the photosensitive drum 1 that has not been transferred is removed by the cleaner 5, the photosensitive drum 1 is charged again by the charger 2, and the above process is repeated. Therefore, the photosensitive drum 1 and the intermediate transfer belt 6
Are rotated four times in synchronization with each other, so that toner images of four colors are superimposed on the intermediate transfer belt 6, and all toner images are combined. When all the toner images are synthesized on the intermediate transfer belt 6, the recording paper 15 is fed out under the control of the control unit.
By applying a voltage having a polarity opposite to that of the toner, for example, about 2 KV to the rear surface of the recording paper 15 by the transfer roller 12, all the toner images are transferred. Then, the recording paper 15 is conveyed to the fixing section 13 where the transferred toner image is fixed. Further, the toner remaining on the intermediate transfer belt 6 without being transferred to the recording paper 15 is removed by the cleaner 14 which operates when the transfer to the recording paper 15 is completed. FIG. 8 is a view for explaining another configuration example of the color image forming apparatus. FIG. 8 shows a case where the intermediate transfer drum 18 is used as an intermediate transfer body. When the intermediate transfer drum 18 is rotated four times in synchronization with the photosensitive drum 1, all toner images are combined on the intermediate transfer drum 18. Other operations are the same as those in FIG. FIG. 9 is a diagram for explaining the detection of exposure start timing. As described above, while the toner image formed on the photosensitive drum 1 is sequentially transferred to the intermediate transfer body for each color, the toner image already transferred on the intermediate transfer body and the toner image to be transferred from now on In some cases, the positions do not completely match, causing color shift of the image. For this reason, as shown in FIG. 9, for example, when the intermediate transfer belt 6 is used for the intermediate transfer member, a marker 16 is provided on the intermediate transfer belt 6, the marker 16 is read by the sensor 7, and a marker detection signal is output. As a trigger, there is a method in which the control unit 17 sends an exposure start command every time to the exposure unit 4 shown in FIG. In an exposure system using a rotating mirror such as a laser optical system, a laser beam scans a line on the photosensitive drum 1 at fixed time intervals, so that print data writing control is performed by a beam detector in the laser optical system. The timing is determined by detecting that the laser beam has reached the end of the line scanning. However, the position of the laser beam at the time when the marker 16 of the intermediate transfer belt 6 is detected is not always constant, and the time from the detection of the marker 16 by the sensor 7 to the actual start of exposure varies for each color. . For this reason, the printing start positions of the respective colors are not aligned, and
A color shift of up to one line has occurred in the sub-scanning direction.
As a countermeasure, conventionally, the time from the marker detection to the detection of the laser beam by the beam detector is detected, and this time is compared with a predetermined reference value to slightly reduce the angle of the mirror in the laser beam optical path. A method of adjusting the print start position by changing the print start position is known in Japanese Patent Application Laid-Open No. 62-267774. As another method, a method has been proposed in which the feed speed of the intermediate transfer body is controlled between the marker detection and the start of exposure to adjust the printing start position. However, by using the above method, it is possible to adjust the print start position, but it is not possible to eliminate all the color shifts in the page. This is because even if the alignment is performed at the leading edge of the page, since the subsequent alignment cannot be controlled, errors accumulate due to various causes, and a color shift occurs at the trailing edge of the page. It is because. A cause of the occurrence of the color misregistration is a speed fluctuation of the intermediate transfer member. This is because, when the intermediate transfer belt 6 is used for the intermediate transfer member, the driving roller 8 and the intermediate transfer belt 6 are used.
And the eccentricity of the driving roller 8 and the fluctuation of the load torque. On the other hand, when the intermediate transfer drum 18 is used for the intermediate transfer member, the eccentricity of the drum, the roundness, the fluctuation of the load torque, and the like are the causes. As described above, the conventional print start position alignment method has a problem that it is not possible to prevent the occurrence of color misregistration in a page. In general, when the intermediate transfer drum 18 is used as the intermediate transfer member, the speed fluctuation is smaller, but the peripheral length of the intermediate transfer drum 18 needs to be longer than the largest recording paper. However, it is difficult to increase the mechanical accuracy until the diameter of the intermediate transfer drum 18 becomes large and sufficient stability is obtained. Therefore, there is a problem that an attempt to increase the mechanical precision will result in a very high cost. In view of the above-mentioned problems, the present invention detects a marker at an equal interval for detecting the speed provided at the end of the intermediate transfer member by using a sensor and converts the marker into a signal. By controlling the speed of the motor that drives the intermediate transfer member so that it matches the frequency and phase of the system line scanning clock, it is possible to economically prevent the occurrence of color misregistration within one page. I have. FIG. 1 is a block diagram for explaining the principle of the present invention. The color image forming apparatus has a first
The image carrier 20 is scanned by the electrostatic latent image forming means 24 to form an electrostatic latent image, developed, transferred to the second image carrier 21, and transferred to the second image carrier 21. The toner image transferred to the recording paper. The configuration of the color image apparatus of the present invention
Scans the first image carrier by electrostatic latent image forming means
After forming and developing an electrostatic latent image, the image is transferred to a second image carrier.
And transfer the toner image transferred on the second image carrier to the recording paper.
A color image forming apparatus for transferring, comprising: a second image carrier
Detects multiple equally spaced markers at the end of the
Multiple marker signal detecting means for conversion, and detected marker
Motor control voltage that converts the frequency of the signal to a predetermined frequency
Frequency control signal output means for generating and outputting a marker signal, and a marker signal
And the reference clock frequency of the electrostatic latent image forming means.
The phase difference is detected based on the
Phase control signal output to generate and output motor control voltage to match
Force means, frequency control signal output means, and phase control signal output
Means for carrying a second image based on each control voltage output by the
Motor drive control means for controlling the body motor.
You. With the above configuration, the toner images of each color formed on the first image carrier 20 are sequentially converted to the second image carrier 21. When the image is transferred to the upper side, alignment is performed at the leading edge of the page, and subsequent alignment can be controlled, so that errors due to the various causes can be canceled. Therefore, it is possible to prevent the occurrence of color shift within one page. FIG. 2 is a block diagram of a circuit showing one embodiment of the present invention. FIGS. 3 and 4 are diagrams for explaining the operation of FIG. 2, and FIGS. 5 and 6 are intermediate diagrams of the present invention. FIG. 3 is a diagram illustrating an example of a transfer body. FIG. 2 shows a case where the intermediate transfer belt 6 is used for the intermediate transfer member. The speed detecting means 22 in FIG. 1 is constituted by the sensor 7, and the driving means 23 in FIG. And a motor. The exposure unit 4 includes a laser diode 40, a lens 41, a polygon mirror 42,
Spindle motor 43, lens 44, mirror 45
And an optical system including the beam detector 46 and the reference oscillator 4
And an exposure control circuit 47 including an exposure control circuit 8. The polygon mirror 42 is, for example, an eight-sided mirror. The polygon mirror 42 is rotated by a spindle motor 43. The laser diode 40 reflects a laser beam projected through the lens 41 and projects it on the mirror 45 via the lens 44. Accordingly, the laser beam reflected by the mirror 45 moves on the photosensitive drum 1 in the main scanning direction, for example, at a resolution of 600.
Line scanning is performed at dpi, and the beam detector 46 detects that the laser beam has reached the end of the line scanning. The spindle motor 43 generates, for example, eight pulses for each rotation and sends it to the exposure control circuit 47. The exposure control circuit 47 divides the pulses and the frequency of, for example, 29.027 MHz generated by the reference oscillation section 48. The spindle motor 43 is rotated at a predetermined rotation speed based on the clock that has been rotated. The photosensitive drum 1 has, for example, a diameter of 80 mm and rotates at a peripheral speed of 120 mm / s. The intermediate transfer belt 6 has, for example, an outer periphery of 251 mm and a thickness of 100 μm.
DC motor 79
Driven by the driving roller 8 driven by the As shown in FIG. 5, the intermediate transfer belt 6 has a marker 16a or 16b at an end.
The marker 16a shown in FIG. 5A has two regions having different light reflectivities, for example, black and white regions, which are alternately painted at equal intervals. It is read as an on / off signal at equal intervals by the sensor 7a. Accordingly, in FIG. 3A, the time t is plotted on the horizontal axis.
When the voltage is plotted on the vertical axis, it is converted into an AC signal as shown by fg in FIG. 3 (A) and sent to the amplification and waveform shaping circuit 71. f
It is converted into a pulse train as shown in _T. The marker 16b shown in FIG. 5B is divided into two regions having different light transmittances at equal intervals, for example, a transparent region and an opaque region. The transparent region and the opaque region are read by the sensor 7b composed of a light receiving element and a light receiving element, and are converted into signals as shown by fg in FIG. . Then, the amplification and waveform shaping circuit 71, is converted into a pulse train as shown in f _T of FIG. 3 (A). FIG. 8 shows a case where an intermediate transfer drum 18 is used as an intermediate transfer member instead of the intermediate transfer belt 6. The end of the intermediate transfer drum 18 is provided with 16c in FIG.
As shown in the figure, a marker 16c is provided, and two regions having different light reflectivities, for example, a black region and a white region are alternately painted at equal intervals. The rotation of the intermediate transfer drum 18 causes the reflection type sensor 7a to read light and shade at equal intervals. As a result, the signal is converted into a signal as shown by fg in FIG. Then, by the amplification and waveform shaping circuit 71, FIG.
It is converted into a pulse train as shown in f _T of (A). [0044] The converted pulse train, if the peripheral speed of the traveling speed or the intermediate transfer drum 18 of the intermediate transfer belt 6 varies, as shown in f _T in FIG. 3 (B), changes the frequency of the pulse train. The FV (frequency-voltage) conversion circuit 72
In response to the fluctuation of the frequency of the input pulse train, for example, as shown by V _AFC in FIG. 3B, when the traveling speed of the intermediate transfer belt 6 or the peripheral speed of the intermediate transfer drum 18 increases, the frequency of the pulse train increases. , So that the voltage decreases. That is, as shown in FIG. 3C, when the frequency f _T is plotted on the horizontal axis and the voltage V _AFC is plotted on the vertical axis, the FV conversion circuit 72 sets the frequency f _T0 at the center. , the higher the voltage the frequency f _T is underspeed side voltage becomes the overspeed side is to have a characteristic to be low. Accordingly, the voltage V _AFC that changes according to the running speed of the intermediate transfer belt 6 or the peripheral speed of the intermediate transfer drum 18 is sent from the FV conversion circuit 72 to the mixing circuit 77. The frequency dividing circuit 74 sends a signal f _T1 obtained by dividing the frequency f _T to a frequency of (1 / integer) to the phase comparing circuit 73. The signal f _{S1 obtained} by dividing the frequency of the clock f _S is compared with the phase
To send to. The frequency dividing ratio of the frequency dividing circuits 74 and 75 is set so that the frequency of the signal f _T1 coincides with the frequency of the signal f _S1 , and the interval between the markers 16a or 16b of the intermediate transfer belt 6 and the intermediate transfer drum The interval between the 18 markers 16c is set to an integral multiple of the line scanning interval of the exposure unit 4. When the resolution is 600 dpi, the marker 16a
Alternatively, if the interval between 16b and 16c is 1.27 mm, for example, this corresponds to 30 times the interval between line scans. Therefore, the traveling speed of the intermediate transfer belt 6 or the intermediate transfer drum 1
If the peripheral speed of 8 is 120 mm / s, the frequency of the signal fg transmitted by the sensor 7 is 94.488 Hz. Therefore, assuming that the frequency division ratio of the frequency dividing circuit 74 is 1/1, the frequency of the signal f _T1 is 94.488 Hz, so that the frequency of the signal f _S1 depends on the exposure control circuit 47 and the frequency dividing circuit 75. 29.027M generated by the reference oscillation section 48
Hz is divided and supplied to 周波 数 × 30 × 128 × 20. As shown in FIG. 4A, when the time t is plotted on the horizontal axis and the voltage is plotted on the vertical axis, the phase comparison circuit 73
And the signal f _S1 transmitted by the frequency dividing circuit 74.
_According to the phase difference with _T1 , the low-pass filter 76
(A) A voltage as indicated by Vp is transmitted. That is, if the phase of the signal f _T1 is ahead of the phase of the signal f _S1 , a pulse is transmitted so as to transmit a voltage lower than the reference value, and the phase of the signal f _T1 is delayed from the phase of the signal f _S1. In this case, a pulse is transmitted so as to transmit a voltage higher than the reference value, and if the phase is the same, only the reference value is transmitted. Accordingly, the low-pass filter 76 has the configuration shown in FIG.
As shown in (B), taking the phase φ on the horizontal axis and the voltage on the vertical axis,
When the phase comparison circuit 73 sends out only the reference value as described above, the control voltage V _APC corresponding to 0 of the phase φ is changed to the mixing circuit 7.
7 and, if there is a phase difference, a control voltage V _APC that changes in accordance with the advance or delay of the phase difference is sent to the mixing circuit 77. Therefore, the mixing circuit 77 _{generates the} signal f _T1 and the signal f _S1.
Of such phases coincide, the control voltage V _APC is an automatic phase control signal for controlling the rotational speed of the DC motor 79, the as the frequency f _T from F over V conversion circuit 72 reaches the set frequency f _T0 As described above, since the control voltage V _AFC which is an automatic frequency control signal for controlling the rotation speed of the DC motor 79 is provided, the frequency and phase of the signal fg read by the sensor 7 are adjusted to the frequency of the clock generated by the reference oscillator 48. And a drive voltage V _C capable of performing frequency-phase synchronization control for controlling the phase to coincide with the phase. Therefore, the motor drive circuit 78 applies the drive voltage V
A drive current for controlling the rotation speed of the DC motor 79 corresponding to _C is sent to the DC motor 79. It is to be noted that the variation of the running speed of the intermediate transfer member that most affects the occurrence of color misregistration is a portion where the intermediate transfer member and the photosensitive drum 1 are in contact. Therefore, it is desirable to detect the speed fluctuation in this portion and control the running speed on the surface of the intermediate transfer member. However, since it is difficult to provide the sensor 7 in this portion, it is preferable to mount the sensor 7 at a position immediately before the surface of the intermediate transfer member contacts the photosensitive drum 1. That is, the mounting position of the sensor 7 shown in FIG. 7 is preferably the position closest to the transfer roller 11a, and the mounting position of the sensor 7 shown in FIG. It is good to set it to the position immediately before touching 1. When the intermediate transfer belt 6 is used for the intermediate transfer member, a delay is not generated until the control result of the DC motor 79 appears at a position where the intermediate transfer belt comes into contact with the photosensitive drum 1.
The drive roller 8 is preferably mounted at a position immediately after the intermediate transfer belt 6 comes into contact with the photosensitive drum 1, that is, a position closest to the transfer roller 11b shown in FIG. As described above, according to the present invention, when the toner images of each color formed on the photosensitive drum are sequentially transferred onto the intermediate transfer member, the toner images are aligned at the leading edge of the page. Since the subsequent alignment control is also performed, it is possible to cancel the traveling speed error between the photosensitive drum and the intermediate transfer member. Accordingly, it is possible to prevent image distortion and color shift within one page.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustrating the principle of the present invention. FIG. 2 is a block diagram of a circuit illustrating an embodiment of the present invention. FIG. 3 is a diagram illustrating the operation of FIG. 1) FIG. 4 illustrates the operation of FIG. 2 (part 2). FIG. 5 is a diagram illustrating an example of the intermediate transfer body of the present invention (part 1). FIG. 6 is an example of the intermediate transfer body of the present invention. FIG. 7 illustrates a configuration example of a color image forming apparatus. FIG. 8 illustrates another configuration example of a color image forming apparatus. FIG. 9 illustrates exposure start timing detection. [Description of Signs] 1 Photosensitive drum 2 Chargers 3a to 3d Developing unit 4 Exposure unit 5, 14 Cleaner 6 Intermediate transfer belt 7, 7a, 7b Sensor 8 Driving roller 9, 10 Stretch rollers 11a, 11b, 12 Transfer Roller 13 Fixing unit 15 Recording paper 16, 16a to 16c Marker 17 Control unit 18 Intermediate transfer drum 20 Image carrier 21 second image carrier 22 speed detecting means 23 driving means 24 electrostatic latent image forming means 40 laser diode 41, 44 lens 42 polygon mirror 43 spindle motor 45 mirror 46 beam detector 47 exposure control circuit 48 reference Oscillator 71 Amplification and waveform formation circuit 72 FV conversion circuit 73 Phase comparison circuit 74, frequency divider circuit 76 Low-pass filter 77 Mixer circuit 78 Motor drive circuit 79 DC motor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-199013 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/525 G03G 15/01 114 G03G 15 / 16

Claims (1)

(57) [Claim 1] A first image carrier is scanned by an electrostatic latent image forming means to form an electrostatic latent image, and after being developed, the electrostatic latent image is formed on the second image carrier. A color image forming apparatus that performs transfer and transfers a toner image transferred onto a second image carrier to recording paper, and detects a plurality of equally-spaced markers provided at an end of the second image carrier. A plurality of marker signal detecting means for converting the frequency of the detected marker signal into a predetermined frequency.
Frequency control signal output means for generating and outputting motor control voltage
Stage, frequency of marker signal and reference clock of electrostatic latent image forming means
The phase difference is detected based on the frequency of the
Phase that generates and outputs the motor control voltage that matches the phase
Control signal output means, frequency control signal output means, and phase control signal output means.
Motor of the second image carrier based on the control voltages output
Color image forming apparatus characterized in that a, a motor drive control means for controlling.